Diffusion transfer thermographic stencil and process



May 5, 1964 K. WOLFSON ETAL 3,131,623

DIFFUSION TRANSFER THERMO'GRAPHIC STENCIL AND PROCESS Filed Oct. 10; 1961 POROUS STENCIL SUPPORT GLAZED SURFACE STENCIL SUPPORT COATED WITH WAX COMPOSITION UNGLAZED SURFACE TRANSFER PROCESS NUCLEATING LAYER COATED STENCIL SUPPORT ORIGINAL TO BE DUPLICATED LIGHT-SENSITIVE COATING PHOTOGRAPHIC PAPER SUPPORT LATENT IMAGES OF TYPED LETTERS IIIIII IIIIIIII PRINTING LIGHT EXPOSURE FIG. 5.

PHOTOGRAPHIC PAPER SUPPORT LIGHT-SENSITIVE COATING NUCLEATING COATING COATED STENCIL DEVELOPED SILVER IMAGES SILVER IMAGED STENCIL BLANK DUPLICATING STENCIL MASTER I-IEAT GENERATING RADIATION SOURCE SILVER IMAGE D LIQUIFIED STENCIL COATING ABSORBENT INVENTORS KURT WOLFSON LUCIAN C. AU TIN OMAR BATUR Y ATTORNEY- ZgM United States Patent 3,131,628 DIFFUi0N TRANSFER THERMOGRAPHIC STENCIL AND PRGCESS Kurt Wolfson and Lucian 6. Austin, Newton, and Omar Baturay, Andover, Ni, assignors to Anken Chemical 8: Film Corporation, Newton, NJ.

Filed Oct. 1t), 1961, Ser. No. 144,160 4 Claims. (Cl. lt)1128.3)

This invention relates to ink-transmitting duplicating stencils and, more particularly, to a new photothermographic stencil and to the process for preparing stencil masters therefrom.

The commonly used method for imaging ink-transmitting duplicating stencils is by cutting or displacing the relatively soft, ink-impervious coating of the stencil support. Such transcribing methods are tedious and time-consuming since each image letter, character symbol or indicating mark of the origin alcopy to be duplicated must be individually cut into the stencil coating, one mark at a time. Furthermore, such cut stencil images are not true facsimile copies of the original copy images but are merely transcribed versions thereof. 1 7

Accordingly, it is an object of this invention to provide an improved process for producing ink-transmitting stencil masters without cutting or otherwise displacing the stencil coating by mechanical means.

A further object is to provide a process for rapidly producing stencil masters having ink-transmitting image areas which are true facsimile copies of original copy images.

A related object of this invention is to provide a new stencil blank material which is stencilized by a novel combination of photographic and thermographic image-forming processes.

In the drawing, g

FIGURE 1' is a schematic crosssectional view on a greatly enlarged scale, of a porous cellular stencil support.

FIGURE 2 is a schematic cross-sectional view showing the stencil support of FIGURE 1 impregnated with a wax composition. FIGURE 3 is another schematic cross-sectional view of the stencil support of FIGURE 2 showing the glazed surliace thereof coated with a transfer process nucleating layer.

FIGURE 4 is a schematic cross-sectional view on a greatly enlarged scale of an original to be duplicated and a photographic paper showing printing light exposure through said photo paper support having a light-sensitive coating thereon, in contact with said original. FIGURE 5 is a schematic cross-sectional view of the exposed and developed photo-graphic paper support of FIGURE 4, showing it in contact with the coated stencil support of FIGURE 3.

FIGURE 6 is a schematic cross-sectional view of the stencil support of FIGURE 3 showing the developed silver image thereon.

FIGURE 7 is a schematic cross-sectional view of the silver imaged stencil support of FIGURE 6 showing it sandwiched between two absorbent sheets and exposed to heat generating radiation. 1

FIGURE 8 is a schematic cross-sectional view on a greatly enlarged scale of the finished duplicating stencil master.

The foregoing objects and advantages of this invention are attained, as illustrated for example in the drawing on ice are attained, as illustrated for example in the drawing on an exaggerated scale, by (a) impregn-athrg a porous cellular stencil support with a molten, continuous film-forrning wax composition coating which is solid at room temperatures and capable of being reduced to the liquid state at elevated temperatures, and glazed onesurface of the coated stencil support, (b) coating the glazed surface of the stencil with a dilfusion transfer process nucleating layer, (0) exposing a layer of light-sensitive silver halide emulsion to the original to be copied to form a latent image of the original in the light-sensitive layer, (d) developing the exposed silver halide emulsion layer in contact with the nucleating layer and in the presence of a silver halide solvent, (2) separating the contacted layers, and (f) exposing the silver imaged stencil master to heatgenerating radiation to. elevatethe temperature of the silver images and. thereby cause the stencil coatingto be reduced to the liquid state coextensively with the silver images and absorbed by Ian adjacentbut separable absorbent material.

Stencil blanks foruse in the present process are prepared by impregnating porous stencil base tissue or-cloth with an inkairnpervious coating of a continuous, film-formingv wax composition which is solid in its normal state at ordinary room temperatures but which is reduced to the liquid state at about F. or higher temperatures and which has a sharp melting point. Suitable film-forming coating compositions are natural and synthetic waxes and wax-like compositions, and mixtures thereof. and include higher fatty acids and their metal. salts, polyolefin and parafiin waxes and solid mixtures of fatty acid esters of higher monohydric aliphatic and phytosterol alcohols, all of which compositions are referred to herein as wax compositions.

The stencil tissue or cloth is completely covered with the Wax composition so that the tissue or cloth acts as a resinforcement for the waxy film. A coating thickness of about 4 mils has been found satisfactory for a readily fusible stencil coating. For wax coating compositions having higher melting points, of the order of 400 to 500 F the coating thickness may be reduced to the, order of 1 to Zmils. However, excess of coating thickness is to be avoided if sharpness of image is desired in the stencilized master; After coating, one surf-ace of the coated stencil is glazed by :ferrotyping or pressing thecoating surface against a polished surface of, for example, a chromium plated roller or drum. l

The glazed surface of the stencil coating is then coated with a thin layer of a colloid containing a nucleating agent, such layer sewing as the reception coating for forming silver images by the diffusion transfer reversal process as described in Rott, US. Patent 2,352,014. In the aforesaid process, a photographic silver halide emulsion is exposed to an image and developed in the presence of a silver halide solvent, while pressed into cont-act with a separable layer of a colloid containing agents which serve to nucleate silver ions which diflfuse into the layer. In the presence of an active photographic developer, a negative image of the original is formed in the photographic emulsion layer and, due to the action of the silver halide solvent, undeveloped, dissolved, silver halides diffuse into the adjacent, nucleating layer and are reduced by the developer to metallic silver, forming a positive, duplicate image of the original. The nucleating layers or coatings o m9 for the diffusion transfer process are also referred to as reception layers or coatings since they serve to receive the migrating silver ions. Nucleating agents for catalyzing the reduction of dissolved silver salts and which thus accelerate and improve the development of silver images in diffusion transfer process reception coatings, comprise physical development nuclei and chemical precipitants for silver ions, and include colloidal silver, silver, colloidal silver sulfide, colloid silver protein complexes such as is known in the pharmaceutical trade as mild silver pro tein, zinc sulfide, cadmium sulfide, organic sulfiding agents such as mercaptates, xanthates, thiourea, and thiourea derivatives, such as allyl thiourea, which react with the dissolved silver halide complex salts to form colloidal silver sulfide; and reducing agents such as sodium stannite, hydrazine and substituted hydrazines, hydroxylamine and derivatives thereof.

The colloid carrier for the nucleating agents of the diffusion transfer reception coatings may be natural or synthetic, film-forming, hydrophilic colloids and polymers, which have protective colloid characteristics, such as gelatin, egg albumin, sodium alginate, casein, polyvinyl alcohol and polyvinyl pyrrolidone.

For optimum sharpness of the stencilized master, it is important to ensure intimate contact of the nucleating layer with the glazed surface of the stencil coating. For the same reason, it is also necessary to have good adhesion between the water-sensitive colloid reception coating and the glazed surface of the wax composition coating, particularly in view of the relatively high alkalinity of the transfer processing solution used to form the silver images in the reception layers. Good adhesion between the nucleating coating and the polished stencil coating is also important to prevent a portion of or even the entire nucleating layer, and the silver images formed therein,

from being pulled away from the stencil coating surface when the developed photographic emulsion layer is stripped away from the surface of the reception coating. To ensure the necessary adhesion, one or more surfaceaotive agents having a high degree of wetting action are incorporated in either the colloid reception coating, the wax composition of the stencil coating, or in both coating compositions. Anionic wetting agents such as sodium tetradecyl sulfate, sodium 2-ethyl-hexyl sulfate and sodium heptadecyl sulfate have been found to be particularly advantageous in obtaining good adhesion between the reception layer and the surface of the stencil coating. Excellent adhesion between the coatings has resulted from the use of a combination of an anionic surface-active agent such as sodium 2-ethyl-hexyl sulfate, in the colloid reception coating and a high molecular weight polyalkylene glycol, such as Carbowax 4000 (Union Carbide Chemicals C0,). The use of a high molecular weight surface-active agent in the wax composition coating has the additional advantage in that the surfactant serves also as a plasticizing agent of the wax composition.

For imaging the novel stencil blanks prepared as herein described, ofiice copying machines which perform the principles of the diffusion transfer process of the aforementioned Rott patent, are admirably suited. In such office copying machines, the light-sensitive photographic printing paper is exposed to the original to be duplicated, the exposed photographic paper and the water-sensitive reception coating of the stencil are then wetted with the transfer processing solution comprising, essentially, a photographic developer containing a silver halide solvent, and then the surface of the exposed coating of the photographic paper, which now contains processing solution, is squeegeed by pressure rollers into contact the reception coating of the stencil blank. After remaining in contact for 10 to 60 seconds, the photographic paper is stripped away from the stencil blank, revealing a developed silver image on the stencil coating, which developed image is a duplicate of the original copy image. Photographic copying machines which perform the functional 5?. principles of the diffusion transfer process are described, for example, in Eisbein, U. S. Patent 2,657,618 and Schwienbacher, US. Patent 2,903,954.

With one surface of the stencil coating provided with a silver image duplicate of the original image copy, the silver images are employed to absorb and concentrate heatgenerating radiation within such images. Upon absorbing heat-generating radiation, the temperature of the silver images is raised substantially above the temperature of the surrounding, non-imaged stencil coating until the melting point of the wax composition coating is reached whereupon the wax composition is reduced to the liquid state coextensively with the silver images. The very thin stratum of colloid which is immediately adjacent the silver images, having been rendered brittle by the heated silver images, is carried away by the liquidized wax composition along with the silver image particles. To insure removal of the liquidized wax coating composition and the entrained silver image and colloid particles, both surfaces of the silver imaged stencil are covered with an absorbent material which has a high transmission factor for the heat-generating radiation. Suitable absorbent materials are one or more thicknesses of absorbent tissue paper, uncoated stencil tissue or lens cleaning tissue paper.

For exposing the silver imaged stencil to heat-generating radiation, a photographic printing box may be used by substituting for the usual light source, an electrically operated incandescent emission source which is rich in infra-red radiation such as, for example, the ordinary incondescent infra-red heat lamps and drying lamps. Other suitable exposing radiation sources include ordinary photographic flash bulbs, in which case a number of the bulbs must be fired simultaneously to provide sufiicient heatgenerating radiation but with such flash-bulb exposure, the final step in producing the stencilized master is practically instantaneous. In place of flash-bulbs or infrared heat lamp bulbs, other incandescent filament lamps operated at higher than rated current densities may also be used. Office copying machines which produce copies on thermographically sensitized copying papers provide convenient means for exposing the present silver imaged stencils to heat-generating radiation. One such suitable type of thermal printing machine is described in Miller, US. Patent 2,740,895. Another suitable thermal exposing device is the Master-Fax duplicator sold by Ditto, Incorporated.

The invention is further illustrated but is not intended to be limited by the following examples wherein all parts and percentages are by weight, unless indicated otherwise.

Example 1 A wax stencil coating composition was prepared by mixing, in the molten state, a relatively soft wax and a hard wax, as follows:

Percent Mobil Wax, M.P. -127" -F 98 Litene OX-88, M.P. 207-217 F 2 [:Socony Mobil Oil (30., Inc.,

New York, New York]. [Petroleum Specialties Inc.,

New York, New York]. The molten wax mixture was applied to a stencil reinforcement of Borlan P 44/45, an ll-gauge (0.01 mm. thickness) white, woven nylon fabric sold by the Borlan Corporation, New York, New York, and having weave of 122 threads per inch warp and 96 threads per inch weft.

The wax mixture was applied to the fabric and, while still in the fluid state, the wax-carrying fabric was passed over a heated roller while a doctor blade removed the excess wax from the opposite surface of the fabric. The wax impregnated fabric then was contacted with the polished surface of a chilled glazing roller to give one surface of the stencil base a smooth, unbroken finish. By this manner of applying and treating the wax-impregnated fabric, the thickness of the impregnated fabric is substantially the same as the thickness of the fabric ma- Egg albumin grams 5.0 Mild silver protein do 2.5 W'ater ml 750 Methyl alcohol ml 187 Ammonium hydroxide ml 2.5 Granulated sugar grams 50.0 Triton W-30 concentrate ml... 4.0

[Sodium salt of an alkyl aryl poflyether sulfate, sold by =Rohm & Haas, Philadelphia, Pennsylvania] The reception coating was rapidly dried with low humidity air at room temperature.

The nucleated stencil blank was converted into an imaged duplicating stencil as follows. A typewritten letter was printed by reflex exposure onto a high contrast, gelatino-silver chloride emulsion coating of photographic printing paper to form a latent image of the original letter. The exposed photographic paper was then moistened with a diffusion transfer developer processing solution of the following composition:

Ethylenediamine tetraacetic acid grams 1.5 Sodium sulfite, anhydrous do 80.0 Sodium hydroxide do 9.0 1-phenyl-3 -pyrazolidone do 1 .6 Hydroquinone do 13.5 Sodium thiosulfate, anhydrous do 10.0 Potassium bromide do 0.6 1-phenyl-S-mercaptotetrazole do 0.1 Water to liter-.. 1

At the same time, the nucleated coating of the stencil blank was also moistened with the same processing solution. Immediately after moistening, the exposed emulsion coating and the nucleated coating of the stencil blank were pressed into intimate contact with each other. Exposure of the photographic printing paper, moistening of the photo-graphic emulsion and nucleated coatings, and contacting the coated surfaces by roller pressure are conveniently performed in any of the commercially available transfer processing machines, such as the Arnpto 12 sold by Ampto Inc., Newton, New Jersey.

The coatings were maintained in contact with each other for about 15 seconds to develop a negative image of the type-written letter in the photographic emulsion coating, and a positive, duplicate image of the letter in the nucleated coating of the stencil blank. The coatings were then stripped apart. In separating the contacted coatings, the wax surface of the stencil blank was held against a flat surface and the developed negative paper was peeled back sharply on itself while maintaining the stencil blank fiat.

After separation, the photographic negative was discarded and the imaged stencil blank was exposed to heat generating radiation to melt the Wax coating coextensively with the silver images in the nucleated coating. To provide for removal of the image-wise fused stencil coating, both sides of the imaged stencil were covered with thin, absorbent tissue paper and then exposure to a source of infra-red radiation was made through the silver imaged coating. Upon removal of the absorbing sheets, a sharp, clear-cut stencil was obtained.

Example 2 It was found that colloidally dispersed particles of silver thiocyanate, precipitated in the presence of a protective colloid such as gelatin, served efiicaciously for nucleating the stencil blank. Colloidally dispersed silver thiocyanate, prepared as described in US. Leermakers Patent 2,221,805, was used to prepare the following nucleating coating composition:

Water ml 900 Albumin grams 9 Colloidal silver thiocyanate do 0.3 Triton W-30 concentrate ml 6 Nylon fabric impregnated with a wax mixture as described in Example 1 was nucleated on the glazed surface with a coated layer of the composition last above described, dried, and provided with a silver image as described in said example. The silver image produced in this nucleated coating containing silver thiocyanate was dark, dense and highly absorbent of heat-generating radiation. The stencil produced by this nucleation was sharp and clean-cut.

Example 3 Using the following as the nucleating coating composition:

Water ml 900 Egg albumin grarns 27 Colloidal silver thiocyanate do 1.3 Triton W-30 concentrate ml 9.0

quite black and very dense silver images on the nucleated surface of the stencil blank were obtained. These black, dense silver images, upon infra-red radiation, produced stencils having extremely sharp and clean-cut imaged openings.

Example 4 Example 5 In place of the wax coating compositions described in the previous examples, the following molten mixture was used:

Percent Stearic acid 40-45 Aluminum stearate 40-45 Japan Wax 10-20 The impregnated stencil base was further coated and processed as described in the preceding examples, and produced a stencilized master having image sharpness of similar quality.

An advantage of the hereinabove described process enables exact facsimile duplicating stencils to be prepared from hand written, printed, typed, sketched or drawn original copies. Another advantage is that the processing solution is the same as is used for making ordinary difiusion transfer copies and thus the processing solu tion in the office copying machines need not be changed for making stencils by the present process, nor discarded after making the stencils in order that the machine can be used for making ordinary transfer copies. A further advantage of the present process is that the silver imaged stencil blanks may be re-exposed to the heat-generating radiation if the initial exposure was not sufficient to completely melt away the wax composition in the silver image areas.

What is claimed is:

l. A photothermographic stencil comprising a porous stencil base impregnated and coated with a heat-fusible wax composition, one surface of said waxed stencil base being glazed and having applied thereto a thin nucleating layer adapted to serve as the reception layer in a silver salt dilfusion transfer process for silver image formation.

2. A photothermographic stencil in accordance with claim 1 wherein the nucleating layer contains colloidal mild silver protein.

3. A photothermographic stencil in accordance With claim 1 wherein the nucleating layer contains colloidal silver thiocyanate.

4. A method of producing an ink-transmitting duplicating stencil, comprising the steps of coating a stencil base with a heat-fusible, ink-impervious wax composition coating which is solid at room temperature, glazing one surface of said coated stencil base, coating said glazed surface with a colloid layer carrying a nucleating agent capable for promoting the reduction of dissolved silver halide complexes without the action of exposing radiation, forming a silver image in the nucleated layer by the diffusion transfer process, exposing the stencil to heat generating radiation to melt said ink-impervious, heat-fusible coating and the colloid carrier layer coextensively with the silver image, and finally removing the melted portions of said heat-fusible, ink-impervious coating and said colloid carrier layer to expose the imaged stencil.

References Cited in the file of this patent UNITED STATES PATENTS 2,352,014 Rott June 20, 1944 2,503,758 Murray Apr. 11, 1950 2,808,777 Roshkind Oct. 8, 1957 2,868,124 Crawford Jan. 13, 1959 2,969,014 Hanson et al Jan. 24, 1961 

1. A PHOTOTHERMOGRAPHIC STENCIL COMPRISING A POROUS STENCIL BASE IMPREGNATED AND COATED WITH A HEAT-FUSIBLE WAX COMPOSITION, ONE SURFACE OF SAID WAXED STENCIL BASE BEING GLAZED AND HAVING APPLIED THERETO A THIN NUCLEATING LAYER ADAPTED TO SERVE AS THE RECEPTION LAYER IN A SILVER SALT DIFFUSION TRANSFER PROCESS FOR SILVER IMAGE FORMATION.
 4. A METHOD OF PRODUCING AN INK-TRANSMITTING DUPLICATING STENCIL, COMPRISING THE STEPS OF COATING A STENCIL BASE WITH A HEAT-FUSIBLE, INK-IMPERVIOUS WAX COMPOSITION COATING WHICH IS SOLID AT ROOM TEMPERATURE, GLAXING ONE SURFACE OF SAID COATED STENCIL BASE, COATING SAID GLAZED SURFACE WITH A COLLOID LAYER CARRYING A NUCLEATING AGENT CAPABLE FOR PROMOTING THE REDUCTION OF DISSOLVED SILVER HALIDE COMPLEXES WITHOUT THE ACTION OF EXPOSING RADIATION, FORMING A SILVER IMAGE IN THE NUCLEATED LAYER BY THE DIFFUSION TRANSFER PROCESS, EXPOSING THE STENCIL TO HEAT GENERATING RADIATION TO MELT SAID INK-IMPERVIOUS, HEAT-FUSIBLE COATING AND THE COLLOID CARRIER LAYER COEXTENSIVELY WITH THE SILVER IMAGE, AND FINALLY REMOVING THE MELTED PORTIONS OF SAID HEAT-FUSIBLE, INK-IMPERVIOUS COATING AND SAID COLLOID CARRIER LAYER TO EXPOSE THE IMAGED STENCIL. 